As disclosed in JP 8-301054, JP 9-104317, JP 10-71911 and DE 10250405, it is known in the prior art that an airbag of a knee-protecting airbag apparatus mounted on a steering column is housed at a lower region of a space inside a column cover in a folded state. In operation, the airbag is fed with inflation gas and emerges from the column cover to be deployed in front of knees of a driver.